1. Technical Field
The present invention relates to a DC/DC converter, a switching power supply device including a plurality of DC/DC converters, and an electronic apparatus using the switching power supply device.
2. Description of the Related Art
With an increase in performance and functionality of mobile devices, a reduction in size and an increase in power capacity of the mobile devices are required. In order to meet the requirements, a DC/DC converter which is provided in the mobile devices needs to have a smaller size, high power capacity, and high efficiency.
In view of the above, a multi-phase power supply technique has been already known in which a plurality of converters are connected in parallel to each other. According to a switching power supply device using the multi-phase power supply technique, a plurality of DC/DC converters are connected in parallel to each other and a predetermined phase difference is given to the switching operations of the DC/DC converters to synchronize the DC/DC converters. The output currents from the plurality of DC/DC converters are combined to reduce a ripple. The technique has an advantage that it is not necessary to use a large passive element in order to form a filter provided in an output unit of the switching power supply device. In addition, the amount of current which flows to each DC/DC converter is less than that when the switching power supply device includes a single DC/DC converter. Therefore, the technique also has an advantage that heat which is generated from each DC/DC converter due to the loss of circuits is reduced and the radiation performance requirements of each DC/DC converter are relaxed. These advantages make it easy to reduce the size of the switching power supply device. In addition, when the power consumption of a load device is small, some of the DC/DC converters are stopped to improve the power conversion efficiency of the entire switching power supply device.
However, in the related art, a dedicated controller needs to be separately used in order to implement the function of the multi-phase power supply. The controller adjusts the output currents from a plurality of DC/DC converters so as to be equal to each other, adjusts the switching time between the DC/DC converters, or stops some of the plurality of DC/DC converters which are connected to each other when the load is small. However, in this case, the number of components increases and wiring between the DC/DC converters and the controller becomes complicated. As a result, the size of the device increases according to circumstances. Therefore, the multi-phase power supply technique is used for a high-capacity power supply device with an output current of several tens of amperes or more and is not capable of being applied as a power supply for a small mobile device with an output current of about several amperes.
In addition, the multi-phase power supply technique according to the related art has the problems that it is difficult to arbitrarily change the number of parallel circuits and to dynamically change the number of parallel operations (the number of phases) depending on a load.
For example, when the switching power supply device is a switching power supply device for a mobile apparatus, it is assumed that the functions of the DC/DC converter is mounted as an integrated circuit (IC). In this case, it is necessary to minimize the number of IC terminals which are additionally required, in order to add a multi-phase function to the converter. For example. in general, a step-down DC/DC convener with an output current of 1 A has a package size of about 2 mm×2 mm and has eight terminals. When the number of terminals increases due to the addition of the multi-phase function, it is necessary to increase the package size, which results in an increase in mounting area.